(a) Technical Field
The present disclosure relates, generally, to a coolant demineralizer for a fuel cell vehicle. More particularly, it relates to a coolant demineralizer for a fuel cell vehicle, which removes released ions from coolant of a fuel cell stack.
(b) Background Art
A fuel cell system employed in a hydrogen fuel cell vehicle as an environment-friendly vehicle comprises a fuel cell stack for generating electricity by an electrochemical reaction of reactant gases, a hydrogen supply system for suitably supplying hydrogen as a fuel to the fuel cell stack, an air supply system for suitably supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, a thermal management system for suitably removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management function, and a system controller for controlling the overall operation of the fuel cell system.
In the above configuration, the fuel cell stack suitably generates electrical energy by the electrochemical reaction of hydrogen and oxygen as reactant gases and discharges heat and water as by-products of the reaction. Accordingly, a system for cooling the fuel cell system to prevent the temperature rise of the fuel cell stack is necessarily required in the fuel cell system.
Preferably, in a typical fuel cell system for a vehicle, a water cooling system for circulating water through a coolant channel in the fuel cell stack is used to cool the fuel cell stack, thus maintaining the fuel cell stack at an optimal temperature.
An exemplary configuration of the cooling system of the fuel cell vehicle is shown in FIG. 1. FIG. 1 is a schematic diagram of a coolant loop of the fuel cell vehicle, which comprises a coolant line 3 disposed between a fuel cell stack 1 and a radiator 2 to circulate coolant, a bypass line 4 and a three-way valve 5 for bypassing the coolant so as not to pass through the radiator 2, and a pump 6 for pumping the coolant.
The applicable materials for pipes, which constitute the coolant loop of the fuel cell system, are limited due to ion release, and include, for example, SUS316L, Teflon, AI 3003, Food-Grade silicon, and the like which have low release rate. Further, it is not possible to use SUS304 due to ion release.
When cheap materials are used, impurities and ions are released from the material which is in contact with the coolant. As a result, the electricity generated from the fuel cell stack may flow through the coolant, which can be problematic.
Further, when the ion conductivity of the coolant is increased by the material used in the fuel cell vehicle, which moves while generating electricity and carrying a driver and passengers, electricity may flow through the coolant loop, which makes it very difficult for the electrical devices and driving components, mounted in the vehicle, to normally operate and further causes a serious danger to the driver and passengers.
As a result, the electrical conductivity of the coolant in the fuel cell vehicle is measured at all times, and a control logic for shutting down the fuel cell system when the electrical conductivity is increased to a predetermined level is employed.
Moreover, a demineralizer 7 is provided in the coolant loop to maintain the ion conductivity of the coolant below a predetermined level.
Preferably, the demineralizer 7 serves to reduce the ion conductivity below a predetermined level by filtering ions contained in the coolant flowing through the fuel cell stack 1. FIG. 2 is a perspective view of a conventional demineralizer, FIG. 3 is a longitudinal cross-sectional view of FIG. 2, and FIG. 4 is a diagram showing a differential pressure region (in which an ion resin is filled) in the conventional demineralizer.
The demineralizer 100 typically comprises a housing 110 through which coolant is passed, an inlet port 120 and an outlet port 130 through which the coolant is introduced and discharged, an ion resin 101 filled in the housing 110 to filter ions contained in the coolant, and mesh assemblies 140a and 140b for supporting the ion resin 101 filled in the housing 110 and preventing the ion resin 101 from leaking.
In the above configuration, the mesh assemblies 140a and 140b serve to suitably pass the coolant and entrap the ion resin 101 in the form of small grains in the housing 110. Preferably, the mesh assemblies 140a and 140b are suitably provided at both the inlet port 120 and the outlet port 130 at both ends of the housing 110 to prevent the ion resin 101 filled in the housing 110 from leaking.
In the demineralizer 100 having the above-described configuration, the coolant introduced through the inlet port 120 (connected to an output of a pump) passes through the mesh assembly 140a, the ion resin 101, and the mesh assembly 140b and is then suitably discharged through the outlet port 130 (connected to an input of the pump) and, while the coolant passes through the ion resin 101, ions are filtered and removed.
The removal of ions from the coolant makes it possible to suitably prevent current leakage from the fuel cell stack, and thereby improve the electrical safety of the vehicle to meet the standard.
However, in the conventional demineralizer 100 shown in FIG. 3, the coolant flows through the longitudinal path between the inlet port 120 and the outlet port 130, and the region, in which the ion resin 101 is filled, along the longitudinal path corresponds to a region in which a difference in coolant pressure (differential pressure) occurs between the inlet side and the outlet side.
As a result, the coolant passing through the region in the longitudinal (axial) direction increases the differential pressure region in the demineralizer (the region in the longitudinal direction in which the ion resin is filled in FIG. 3), and thus a considerable difference in pressure occurs between the coolant introduced through the inlet port and the coolant discharged through the outlet port.
FIG. 5 is a graph showing an increase in differential pressure with respect to an increase in coolant flow rate in the conventional demineralizer, from which it can be seen that a large differential pressure is formed when the flow rate of coolant is increased.
It is known that when the coolant passes through an ion resin layer in the longitudinal direction, a region of the ion resin layer, in which the coolant introduced through the inlet port is filtered, i.e., the width of the ion resin layer, which actually removes ions, on the coolant flow path in the longitudinal direction, is about 15 to 30 mm.
The ion resin in the downstream beyond the width of the ion resin layer, which actually removes ions, shows a low filtering effect, and thus it is not necessary to increase the length of the ion resin layer as much as the longitudinal length of the housing. The ion resin in the downstream other than the region which contributes to the actual filtering is unnecessary.
Accordingly, in the case of the demineralizer configured such that the coolant is suitably introduced through one end of the housing, passes through the ion resin layer in the longitudinal direction, and reaches the other end of the housing, an excessive amount of the ion resin is used, which increases the manufacturing cost and significantly increases the differential pressure.
Further, while the ion resin layer in the vicinity of the outlet port, through which the coolant is suitably discharged, is not used for the filtering of ions, the ion resin layer in the vicinity of the inlet port, through which the coolant is suitably introduced, is mainly used for the filtering of ions.
Therefore, when the demineralizer should be replaced with new one due to a long-term use of the ion resin in the vicinity of the inlet port, it is necessary to replace the entire demineralizer with new one, although the ion resin in the vicinity of the outlet port is still usable, which increases the maintenance costs.
Further, as shown in FIG. 1, the conventional demineralizer is suitably mounted in a bypass loop, not in a main coolant loop, and a high differential pressure is formed due to the long length of the differential pressure region in the ion resin layer. As a result, it is very difficult to effectively circulate the coolant.
In particular, the problem that the coolant does not flow smoothly considerably reduces the effect of filtering ions, and as a result the electrical conductivity is not considerably reduced during initial start-up of the vehicle. As a result, it is difficult to prevent current leakage.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.